The difference between the ntpd calculated frequency and the local system clock frequency (usually in parts per million, ppm)
jitter, dispersion
The short term change in a value. NTP measures Local Time Jitter, Refclock Jitter, and Server Jitter in seconds. Local Frequency Jitter is in ppm or ppb.
kurtosis, Kurt
The kurtosis of a random variable X is the fourth standardized moment and is a dimension-less ratio. ntpviz uses the Pearson's moment coefficient of kurtosis. A normal distribution has a kurtosis of three. NIST describes a kurtosis over three as "heavy tailed" and one under three as "light tailed".
ms, millisecond
One thousandth of a second = 0.001 seconds, 1e-3 seconds
mu, mean
The arithmetic mean: the sum of all the values divided by the number of values. The formula for mu is: "mu = (∑xi) / N".
ns, nanosecond
One billionth of a second, also one thousandth of a microsecond, 0.000000001 seconds and 1e-9 seconds.
percentile
The value below which a given percentage of values fall.
ppb, parts per billion
Ratio between two values: 1 ppb = one in one billion = 1/1,000,000,000 = 1e-9 = 0.0000001%
ppm, parts per million
Ratio between two values: 1 ppm = one in one million = 1/1,000,000 = 1e-6 = 0.0001%
refclock
Reference clock, a local GPS module or other local source of time.
remote clock
Any clock reached over the network, LAN or WAN. Also called a peer or server.
time offset
The difference between the ntpd calculated time and the local system clock's time. Also called phase offset.
σ, sigma
Sigma denotes the standard deviation (SD) and is centered on the arithmetic mean of the data set. The SD is simply the square root of the variance of the data set. Smaller is better. The formula for sigma is: "σ = √[ ∑(xi-mu)^2 / N ]".
skewness, Skew
The skewness of a random variable X is the third standardized moment and is a dimension-less ratio. A normal distribution has a skewness of zero.
upstream clock
Any server or reference clock used as a source of time.
μs, us, microsecond
One millionth of a second, also one thousandth of a millisecond, 0.000001 seconds, and 1e-6 seconds.
